What causes slipped strand Mispairing?
It is a form of mutation that leads to either a trinucleotide or dinucleotide expansion, or sometimes contraction, during DNA replication. A slippage event normally occurs when a sequence of repetitive nucleotides (tandem repeats) are found at the site of replication.
Is phase variation random?
Phase variation in bacteria is often considered a random process that has evolved to facilitate immune evasion in a host. Here, alternative biological roles for this process are presented and discussed, incorporating recent studies on nonpathogenic and commensal bacterial species.
Is phase variation reversible?
Phase variation in general refers to a reversible switch between an “all-or-none” (on/off) expressing phase, resulting in variation in the level of expression of one or more proteins between individual cells of a clonal population.
What is phase variation in microbiology?
In biology, phase variation is a method for dealing with rapidly varying environments without requiring random mutation. It involves the variation of protein expression, frequently in an on-off fashion, within different parts of a bacterial population.
What result is characteristic of slipped-strand mispairing mutation?
What result is characteristic of slipped-strand mispairing mutation? A protein that, starting at the point of the deletion, has incorrect amino acids and is of abnormal length.
How does slipped-strand replication contribute to genetic variation at repetitive sites in our genome?
Slipped-strand nucleotide mispairing can generate variation in gene expression. Illegitimate base pairing in regions of repetitive DNA during replication, coupled with inadequate DNA mismatch repair systems, can produce deletions or insertions of repeat units.
What is the difference between phase variation and antigenic variation?
Phase variation or phenotypic switch allows the expression of a given phenotype to be switched ON or OFF. Antigenic variation refers to the expression of a number of alternative forms of an antigen on the cell surface, and at a molecular level, shares common features with phase variation mechanisms.
What are phase variable genes?
Phase-variable genes typically encode bacterial surface structures, such as adhesins, pili, and lipooligosaccharide, and provide an extra contingency strategy in small-genome pathogens that may lack the plethora of ‘sense-and-respond’ gene regulation systems found in other organisms.
What result is characteristic of slipped-strand mispairing mutation quizlet?
When a tautomeric shift occurs what is true about the resulting mutation?
When a tautomeric shift occurs, what is TRUE about the resulting mutation? 1. The resulting mutation is always corrected by DNA polymerase’s proofreading ability.
Why does forward slippage lead to deletion?
When the polymerase slips forward (B), it skips one of the template GTA repeats, with only three repeats copied into the newly synthesized DNA strand (i.e., deletion of one repeat). Correspondingly, when the polymerase slips backward (C), it copies an extra repeat into the newly synthesized DNA strand.
What is antigenic phase variation?
Antigenic variation or antigenic alteration refers to the mechanism by which an infectious agent such as a protozoan, bacterium or virus alters the proteins or carbohydrates on its surface and thus avoids a host immune response, making it one of the mechanisms of antigenic escape. It is related to phase variation.
What is an example of antigenic variation?
Examples of random antigenic variation are those that occur in viruses such as the influenza virus and the human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome (AIDS). The major antigenic components of these viruses are glycoproteins that make up their viral coat.
What is phase variation in Salmonella?
The alternative expression of Salmonella genes H1 and H2, which specify different flagellar antigens, results in the oscillation of phenotype known as phase variation. This alternation is controlled by the inversion of an 800-base-pair sequence of DNA adjacent to, or including part of, the H2 gene.
What result is characteristic of slipped strand Mispairing mutation?
What is the only type of mutation that can arise from Mispairing due to tautomeric shifts?
transition mutation – change of one purine/pyrimidine pair to the other purine/pyrimidine pair. This can happen when one base member of a complementary pair undergoes a tautomeric shift during DNA replication, causing it to mispair.
What are the 2 types of frameshift mutations?
Frameshift mutations occur in two types – insertion mutations and deletion mutations. The overall effect of both is similar – the translational reading frame is “shifted” out of alignment, resulting in a random amino acid sequence.
What is slippage during replication?
Replication slippage or slipped-strand mispairing involves the misalignment of DNA strands during the replication of repeated DNA sequences, and can lead to genetic rearrangements such as microsatellite instability.
What is antigenic and phase variation?
What causes antigenic variation?
Antigenic variation can occur by altering a variety of surface molecules including proteins and carbohydrates. Antigenic variation can result from gene conversion, site-specific DNA inversions, hypermutation, or recombination of sequence cassettes.